osf_getdomainname(): use copy_to_user()

BugLink: https://bugs.launchpad.net/bugs/1792419

commit 9ba3eb51 upstream.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

arch/alpha/kernel/osf_sys.c

@@ -561,25 +561,20 @@ SYSCALL_DEFINE0(getdtablesize)
  */
 SYSCALL_DEFINE2(osf_getdomainname, char __user *, name, int, namelen)
 {
-	unsigned len;
-	int i;
+	int len, err = 0;
+	char *kname;
 
-	if (!access_ok(VERIFY_WRITE, name, namelen))
-		return -EFAULT;
-
-	len = namelen;
-	if (len > 32)
-		len = 32;
+	if (namelen > 32)
+		namelen = 32;
 
 	down_read(&uts_sem);
-	for (i = 0; i < len; ++i) {
-		__put_user(utsname()->domainname[i], name + i);
-		if (utsname()->domainname[i] == '\0')
-			break;
-	}
+	kname = utsname()->domainname;
+	len = strnlen(kname, namelen);
+	if (copy_to_user(name, kname, min(len + 1, namelen)))
+		err = -EFAULT;
 	up_read(&uts_sem);
 
-	return 0;
+	return err;
 }
 
 /*